Recent improvements in their spatial and data resolution capabilities have made digital color image processing systems particularly attractive for a variety of photo-processing (e.g. photo-finishing) applications. In still color image photography, for example, once an image (such as that captured on color photographic film or a high resolution color digital camera) has been digitized and stored in an attendant data base, it is readily optimized for reproduction by means of photo-finishing image processing software. One example of a color photo-finishing system that takes advantage of this capability is disclosed in co-pending patent application Ser. No. 582,305, filed Sep. 14, 1990, by S. Kristy entitled "Multiresolution Digital Imagery Photofinishing System," assigned to the assignee of the present application and the disclosure of which is herein incorporated.
As described in that application, conventional photo-finishing of consumer-generated still color photographs (e.g. those captured on 35 mm color film) involves the use of an analog electro-optic system and an associated chemical-based print developing unit. In the above-referenced Kristy application, there is described a digital image-based photofinishing apparatus that enables the user (which may be an unskilled consumer) to personally customize and obtain high quality prints of photographic images; it also provides for the storage and retrieval of high resolution digitized color still images for playback to a variety of reproduction devices.
To this end, as diagrammatically illustrated in FIG. 1, the improved photofinishing apparatus employs a high resolution opto-electronic film scanner 12, the output of which is coupled to a host digitized image processor (host computer) 14. Scanner 12 may comprise a commercially available Eikonix Model 1435 high resolution scanner, having a very high resolution sensor pixel array (a 3072.times.2048 pixel matrix) capable of generating high spatial density-representative output signals which, when converted into digital format, yield `digitized` photographic image files from which high quality color prints may be obtained. Scanner 12 is arranged to be optically coupled with a photographic recording medium, such as a consumer-supplied 35 mm color film strip 16. Film strip 16 typically contains a plurality (e.g. a set of twenty-four or thirty-six) 36 mm.times.24 mm color image frames. For each scanned image frame, scanner 12 outputs digitally encoded data, representative of the opto-electronic response of its high resolution imaging sensor pixel array, onto which a respective photographic image frame of film strip 16 is projected by the scanner's input lens system.
This digitally encoded data, or `digitized` image, is supplied in the form of an imaging pixel array-representative bit map, resolved to a prescribed code width (e.g. eight bits per color per pixel), to host processor 14. Host processor 14 contains an image encoding and storage operator through which each high resolution digitized image file is stored in a multiresolution, hierarchical format. The use of a multiresolution storage format facilitates retrieval of images for reproduction by a variety of devices the resolution of which may vary from device to device, such as a low/moderate NTSC television monitor or a very high resolution, digitally driven, color thermal printer.
One example of a preferred encoding and storage operator that may be used for this purpose is described in U.S. Pat. No. 4,969,204, entitled "A Hybrid Residual-Based Hierarchical Storage and Display Method for High Resolution Digital Images in a Multiuse Environment," by Paul W. Melnychuck et al, assigned to the assignee of the present application and the disclosure of which is herein incorporated.
As described in that application, an original 2048.times.3072 (2K.times.3K) high resolution image may be sequentially `down-converted` into a hierarchical set of respectively different resolution residue images and a base resolution image file. The base file may comprise a 512.times.768 pixel array file formatted as a set of four interlaced (256 lines by 384 pixels/line) lowest resolution image sub-arrays, respectively corresponding to odd pixel/odd line, odd pixel/even line, even pixel/odd line, even pixel/even line sub-arrays. One of the lowest resolution image 256.times.384 sub-arrays is suitable for preliminary display on an NTSC-quality video monitor, while the full 512.times.768 base resolution array provides a high quality image on a an NTSC video monitor. An individual lowest resolution 256.times.384 sub-array may be further sub-sampled to obtain one or more lower resolution files (e.g. a 128.times.192 pixel sub-array) for supporting the display of one or more relatively smaller images, as will be explained below. The spatial parameters of each of the hierarchical image files into which an original 2K.times.3K file is encoded and stored are chosen to facilitate the implementation and incorporation of a low cost, reduced complexity frame store/data retrieval architecture into a variety of reproduction devices, thereby providing for rapid call-up and output (display or print out) of one or more selected images.
For this purpose, host computer 14 may be interfaced with one or more interactive video display terminals (VDTs) or workstations 18 through which digitized image files may be controllably called up for display to a user, in the course of customizing the image prior to further storage or print out. Host computer 14 may also be coupled to drive an optical compact disc recorder 19, or a high resolution output reproduction device, such as digitally driven color thermal printer 20. In a commercial photofinishing application, thermal printer 20 may be used to output a hard copy color print of the digitized image for a customer who has delivered one or more rolls of 35 mm film to the photofinisher for processing.
Where the customer supplies a previously prepared optical disc, the disc is inserted in a disc reader 21, which may be coupled to the host computer 14 or VDT 18. In this application, the control mechanism that drives the video display terminal may contain a simplified or edited version of bit map manipulation software, such as that supplied by a computer graphics vendor, which provides the photofinishing operator with the ability to access menu-driven image manipulation functions, such as the addition of text to the image, zoom, crop, and tone and color corrections of a low resolution (128.times.192) image of a selected file. Once the user is satisfied with what is displayed on the screen, its corresponding highest resolution image (2K.times.3K) image is processed using workstation-entered selections to drive an associated high resolution digital color printer 20, which produces a high quality hard copy print of the processed digital image.
Non-limitative examples of readily coded image processing algorithms that may be used for this purpose include those described in the published literature, such as "Digital Image Processing" by William K. Pratt, in particular, Chapters 4, 12 and 16, respectively entitled "Image Sampling and Reconstruction," "Image Enhancement" and "Luminance, Color, and Spectral Image Restoration," 1978 John Wiley and Sons, ISBN 0-471-01888-0; and "Digital Image Processing" by Rafel C. Gonzalez, in particular, Chapter 4, entitled "Image Enhancement," 1983 Addison-Wesley Publishing Company, Inc. ISBN 0-201-02596-5. Many of such image processing algorithms have been implemented as commercially available packages (which perform all functions on the highest resolution data, so that, without the hierarchical scheme employed in the above-referenced Melynchuck application, they are slower). Their encoding schemes are optimized for performance and are commercially available as libraries of subroutines, such as MathPAK 87 (a trademark of Precision Plus Software). Additional image processing software that may be used includes Photoshop (trademark of Adobe Systems Incorporated), ColorStudio (trademark of Letraset) and PhotoMac (trademark of Avalon Development Group).
Now although a high spatial resolution digital output device, such as a digital thermal color printer, is able to provide a high quality hard copy of a customized image directly from the digital data base, it is relatively slow. Also, because the output reproduction medium (e.g. thermal color print paper) upon which the image is written, is not inexpensive, the price per print remains substantially high, regardless of the number of copies made.
In a conventional analog optical/chemical photo-finishing process, on the other hand, multiple copies of an original image can be made through repeated illumination of a negative onto sheets of relatively inexpensive photo-sensitive color print paper, such as Ektacolor (Trademark Eastman Kodak Co.) color print paper and chemically developing the exposed sheets during a reasonably abbreviated processing sequence. Unfortunately, purely optical/chemical processing systems do not offer the flexibility and processing capability of digital image processing systems.